FXUS64 KBMX 070407
AFDBMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
940 PM CST SUN DEC 6 2009
.UPDATE...EVENING DISCUSSION.
&&
.DISCUSSION...
EXTREMELY DRY OUT THERE THIS EVENING AS 00Z SOUNDING HAD A PW OF
0.15 OF AN INCH...WHICH IS A SLIGHT INCREASE FROM 12Z SOUNDING. AN
UPPER-LEVEL SHORT-WAVE TROUGH HAS NOW EXITED THE FORECAST AREA.
CLOUD COVER HAS DECREASED DRAMATICALLY BEHIND THE SHORT WAVE.
LOW-LEVEL FLOW HAS RETURNED OFF THE WESTERN GULF OF MEXICO...AND
MOISTURE AND WARM-AIR ADVECTION WERE RAMPING UP TO OUR WEST.
HOWEVER...DON'T EXPECT MOISTURE ADVECTION TO REACH WESTERN SECTIONS
OF ALABAMA UNTIL LATE TONIGHT...OR TOWARD 12Z. WILL LEAVE JUST A
SLIGHT CHANCE OF SHOWERS IN THE FORECAST FOR AFTER 09Z TONIGHT. NO
OTHER CHANGES AT THIS TIME.
03
PREVIOUS DISCUSSION...
WOW. FAST MOVING SYSTEMS AND ACTIVE WEATHER PATTERN ALL MAKE FOR A
RATHER CHALLENGING FORECAST OVER THE NEXT 7 DAYS. THERE ARE TWO
MAIN SYSTEMS OF CONCERN DURING THAT TIME...ONE THAT COULD BRING US
SOME SEVERE WEATHER LATE TUESDAY INTO EARLY WEDNESDAY...AND THE
OTHER THAT WILL BRING MORE RAIN...AND A POSSIBLE CAD WEDGE WITH
TEMPERATURES PERILOUSLY CLOSE TO FREEZING FOR A TIME TOWARD THE
END OF THE WEEK.
CURRENTLY...CONDITIONS REMAIN RATHER CHILLY WITH THICK CLOUDS
GATHERING TO THE WEST. WEAK SHORTWAVE PASSING THROUGH TONIGHT AND
MONDAY WILL BRING INCREASING CHANCES OF RAIN. ALTHOUGH POPS WILL
BE IN THE LIKELY CATEGORY FOR MUCH OF THE AREA ON MONDAY...THE
RAIN WON'T BE AROUND FOR ALL THAT LONG...NOR WILL AMOUNTS BE ALL
THAT MUCH. THERE'S A BIT OF A LULL IN THE PRECIP MONDAY
EVENING...BEFORE THE NEXT SYSTEM REALLY GETS CRANKED UP ON TUESDAY.
ALTHOUGH THE BULK OF THE UPPER LEVEL ENERGY ASSOCIATED WITH THE
TUESDAY/WEDNESDAY SYSTEM IS FORECAST TO PASS JUST TO OUR
NORTH...THE AMOUNT OF LOW LEVEL FORCING AND OTHER FACTORS ALL
POINT TO TUESDAY BEING A RATHER RAIN FILLED DAY. AS SUCH...THERE
IS REALLY NOT MUCH OPPORTUNITY TO DESTABILIZE...AND I GET THE
FEELING THAT THERE WON'T BE MUCH (IF ANY) THUNDER AROUND DURING
THIS PHASE OF THIS SYSTEM.
HOWEVER...OVERNIGHT TUESDAY NIGHT THE LOW LEVEL JET REALLY GETS
CRANKED UP AS THE SURFACE CYCLONE INTENSIFIES AND MOVES TOWARDS
THE GREAT LAKES. MODEL SOUNDINGS SHOW THE "GREATEST" AMOUNT OF
CAPE OCCURRING DURING THE OVERNIGHT HOURS. BUT THAT IS STILL A
MODEST 400-800 AT MOST. BUT WITH SHEAR VALUES THROUGH THE ROOF...
ANY SURFACE BASED UPDRAFTS THAT CAN BECOME SUSTAINED WILL BE PRONE
TO START ROTATING. THUS...WE WILL CONTINUE TO MENTION THE
POSSIBILITY OF SEVERE STORMS (INCLUDING THE THREAT OF TORNADOES) IN
THE HAZARDOUS WEATHER OUTLOOK. ALSO...I AM STILL A BIT LEARY OF
THE POSSIBILITY OF EVERYTHING BEING DELAYED MORE INTO
WEDNESDAY...WHICH WOULD GIVE THE LOW LEVELS A BIT MORE OPPORTUNITY
TO DESTABILIZE. BY LATE WEDNESDAY AFTERNOON...WE SHOULD BE
EXPERIENCING RATHER STRONG COLD ADVECTION IN THE WAKE OF THE COLD
FRONTAL PASSAGE.
THURSDAY IS AN IN BETWEEN DAY...WITH THE NEXT SYSTEM SLATED TO
COME IN HERE FRIDAY INTO SATURDAY. THIS SYSTEM IS A BIT MORE
SUBTLE IN ITS FEATURES...AND INVOLVES A WEAKER SOUTHERN STREAM
SHORTWAVE. ONE THING OF DISCONCERTING NOTE IS THE WAY THE EUROPEAN
MODEL BUILDS HIGH PRESSURE ALONG THE EAST COAST...WHILE THE NEXT
OVERRUNNING BATCH OF RAIN BREAKS OUT FRIDAY NIGHT INTO SATURDAY
MORNING. THIS SETS UP WHAT COULD BECOME QUITE A STRONG IN SITU
TYPE CAD WEDGE...WHICH DURING THE (METEOROLOGICAL) WINTER MONTHS
ALWAYS NEEDS TO BE WATCHED. I WAS A LITTLE THROWN BACK BY THE
CATEGORICAL POPS THE GFS MOS SPIT OUT FRIDAY NIGHT. BUT THIS WAS
WELL SUPPORTED BY THE 12Z ECMWF...SO I PUT MY CHIPS ALL IN WITH
THAT WET SOLUTION. THERE'S INCREASINGLY WARM AIR IN THE 850 MB
RANGE...AND SURFACE TEMPS ARE FORECAST TO ALSO STAY ABOVE
FREEZING. SO...A COLD RAIN IS FORECAST.
/61/
&&
.AVIATION...00Z TAF DISCUSSION.
NOT EXPECTING ANY AVIATION PROBLEMS AT LEAST THROUGH MOST OF THE
PERIOD. THE ONLY QUESTION MARK IS WHEN THE RAIN WILL BEGIN TO MOVE
IN. GIVEN THE DRY CONDITIONS CURRENTLY IN PLACE...IT WILL TAKE A
WHILE BEFORE CONDITIONS BECOME MOIST ENOUGH TO ALLOW RAIN TO FALL.
FOR NOW...LEFT VCSH OVER TCL...BHM...AND EET BUT CONFIDENCE ON THIS
TIMING IS LOW. WILL ADJUST THE FORECAST IF NEEDED ON THE NEXT
PACKAGE IF COMPUTER MODELS BECOME MORE IN AGREEMENT.
10/ARM
&&
.BMX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
